Understanding the Function of SpoIIIL during Spore Development
- Publication Type:
- Thesis
- Issue Date:
- 2023
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Sporulation in Bacillus subtilis is an alternative developmental pathway that encompasses several complex cellular events involving hundreds of genes many of which have poorly understood functions. The focus of this project was to unravel the functions of SpoIIIL, a recently discovered 59 amino acids, 9.6 kDA protein, transcribed during sporulation under the control of sigma F, and is believed to be a component of the SpoIIIA-SpoIIQ (A-Q) complex from the forespore compartment.
Here, we report that SpoIIIL is required for spore shape, functions in the monitoring, regulation, and signalling of cortex assembly, ensures the timely activation of sigma G, is not surface exposed, and is unlikely a component of the A-Q complex. And that the precipitation of SpoIIIL from the forespore inner membrane where it is uniformly localized prior to the commencement of cortex assembly, into the forespore cytoplasm where it looks like intriguing patchy-like structures as the result of a SpoIVB-mediated proteolytic event, is the prime indicating signal for the assembly of the cortex.
This work revealed that the proper localization of SpoIIIL depends on SpoIVB, SpoIVA, SpoVM, SpoVD, and SpoVE while the stability of SpoIIIL depends only on SpoIVB, SpoIVA, SpoVM, as well as SpoVID. How cells achieve the coordination between coat and cortex assembly across the intermembrane space still remains largely unclear. Furthermore, we found that cortex assembly was obliterated in the absence of both spoIIIL and the peptidoglycan synthesis gene murAB, and that spores of the ΔspoIIIL ΔmurAB double mutant could not become phase bright. The ΔspoIIIL ΔmurAB double mutant spores did not survive the heat kill treatment or sporulation efficiency assay, ultimately yielding nil or dead spores compared to either the ΔmurAB single mutant which had ~44% sporulation efficiency or the ΔspoIIIL single mutant spores which had ~47% sporulation efficiency. Collectively, the accumulated evidence from this work has provided a significant leap in our understanding of spore development through the mid-stages to the later stages of sporulation in spore forming bacteria. Because, if spore formation can be totally eliminated as is the case in this study, whilst allowing the attainment of all the benefits obtainable from diverse applications of industrially, medically, and environmentally beneficial spore forming bacteria, and the recurrence and transmission of infections by pathogenic spore forming bacteria completely prevented, then we have achieved a milestone in the study of cell differentiation in prokaryotes.
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